1. Field of the Invention
This invention relates to a resin composition excelling in heat resistance and moisture resistance and obtained by using an acrylic resin of a specific structure as a binder resin and adding thereto a dye possessing the largest absorption at wavelengths in the range of 380–780 nm and an optical filter and a plasma display both using the resin composition.
2. Description of the Related Art
In recent years, the PDP (plasma display panel) which enjoys a thin build and is adopted wide screens has been attracting attention. The PDP emits a near infrared ray during the course of plasma discharge. The fact that this near infrared ray induces such electrical apparatus as household TV sets, coolers, and video decks to malfunction has been posing a problem.
With a view to solving this problem, an invention which relates to a near infrared ray blocking film possessing high degrees of near infrared ray intercepting property and visible light transmitting property has been introduced (the JP-A-2001-133624). This patent document-discloses an infrared ray absorbing filter which has the difference between the largest and the smallest of transmittance and the largest transmittance in the near infrared ray region of wavelengths in the range of 850–1100 nm, the lowest transmittance in the visible region of wavelengths in the range of 450–650 nm, etc. set respectively in specific ranges. This invention purports that the infrared ray absorbing filter, when used in a plasma display, is enabled to absorb an unnecessary infrared ray radiated from the display and prevent the remote control using an infrared ray from malfunctioning by setting the difference between the largest and the smallest transmittance and the largest transmittance in the near infrared ray region of wavelengths in the range of 850–1,100 nm and, when installed in the front surface of the display, is enabled to secure brightness by setting the lowest transmittance in the visible region of wavelengths in the range of 450–650 nm. As infrared absorbing dyes, diimonium salt compounds, fluorine-containing phthalocyanine compounds, thionickel complex compounds, etc. are used. As binder resins, polyester type, acrylic type, and polyamide type resins have been disclosed.
In the meantime, a near infrared absorbing filter that an image is clarified by selectively absorbing the so-called neon orange light (in the region of 550–620 nm) liable to obscure the image as well as absorbing the near infrared ray for the purpose of preventing the conventional remote control device from malfunctioning without suffering the other visible light region to be substantially absorbed has been introduced (the JP-A-2002-200711). In the patent document, since the dye which is used for absorbing the neon orange light is deficient in weatherability and durability, a near infrared ray absorbing material which is obtained by having at least a transparent resin coating film containing a near infrared ray absorbing dye and a tackiness agent layer containing a dye capable of selectively absorbing wavelengths in the range of 550–620 nm superposed on a transparent substrate in an order allowing the tackiness agent layer to form the outermost layer is proposed. In the official gazette, the near infrared ray absorbing dye to be used is aimed at a dithiol nickel complex of a specific structure and a diimonium compound of a special structure, the dye capable of selectively absorbing the neon orange light (the region of wavelengths of 550–620 nm) is aimed at a cyanine dye of a specific structure, and the transparent resin is commended to be selected from among polyethylene terephthalate, polyethylene naphthalate, and polycycloolefins from the viewpoint of the stability of dye. The tackiness agent layer is obtained by dissolving the dye and the transparent resin mentioned above in an organic solvent and molding the resultant solution into a film with a roll coater. As the solvent, the use of 1,3-dioxolan or dichloromethane is mentioned.
As regards the optical filter to be disposed in front of the plasma display panel, an invention which is directed to using an optical filter incorporating therein a dye having the maximum absorption at wavelengths in the range of 570–600 nm for the purpose of absorbing such,wavelengths as degrade the color reproducibility in the proximity of the neon orange color that falls in the neighborhood of 590 nm has been disclosed (the JP-A-2001-228323). The patent document concerns the preparation of a PDP filter excellent in color reproducibility owing to the incorporation of a dye having the maximum absorption at wavelengths in the range of 570–600 nm in a transparent acrylic tackiness agent or a methacrylic resin with the object of improving the PDP in the emission spectrum and providing a PDP filter endowed with an enhanced color reproducibility.
A color adjusting filter which exhibits a sharp absorption in the regions of 480–520 nm and 550–610 nm of the light transmission curve and having an absorption in the wavelengths range of 380–420 nm without effecting the three primary colors, ie red, blue, and green has been also disclosed (the JP-A-2003-36033). In this official gazette, as a means to attain the absorption of the neon orange light, an effort to formulate the combination of a tetraazaborphyn type dye of a specific structure, a dipyrazoline type dye of a specific structure, a dipyrazolyl squalilium type dye of a specific structure, etc. and improve the color purity and the range of color reproduction is taught.
Further, a near infrared ray cutting material obtained by superposing on a transparent substrate a transparent resin coating film containing at least a near infrared absorption dye and a dye having the maximum absorption wavelengths in the range of 550–620 nm and consequently enabling the amount of the residual solvent in the transparent resin coating film to reach a level of not less than 5 wt. ppm and less than 500 wt. ppm has been introduced (the JP-A-2002-264278). It has been materialized in view of the fact that the molded article obtained by applying a composition having the near infrared ray absorbing dye mentioned above dispersed in a binder resin and drying the applied layer of the composition is at a disadvantage in revealing deficiency in the stability of the dye in the resin coating film, suffering the performance of near infrared ray absorption to decline and the color hue to change, and exhibiting inferior heat resistance. As concrete examples of the transparent resin to be used, polycarbonate and polyallylate are cited. As concrete examples of the near infrared absorbing dye, dithiol metal complex type, diimonium type, and phthalocyanine type dyes are cited. As concrete examples of the dye possessing the maximum absorption wavelengths in the range of 550–620 nm, cyanine type, squalium type, azomethine type, and xanthene type dyes are cited. As concrete examples of the solvent, THF, diethyl ether, and chloroform are mentioned.
Further, in view of the fact that when an infrared ray absorbing agent is contained in a polyurethane resin layer or other resin layer, the absorbing agent reveals deficiency in heat resistance and durability and suffers the effect of blocking the infrared ray to degrade with the elapse of time, an optical film containing as a main component a thermoplastic resin having a glass transition point in the range of 120–180° C. has been disclosed (the JP-A-2003-4939). It has a statement, reading in effect that if the glass transition point falls short of 120° C., the dye mixed therein will be deficient in durability and weatherability and the dye will be degraded by aging under the conditions of high temperature and high humidity. As concrete examples of the thermoplastic resin of this kind, polyester type resins, olefin type resins, cycloolefin type resins, and polycarbonate resins are cited. Then, as concrete examples of the color hue correcting agent which is capable of absorbing light of wavelengths in the range of 380–780 nm, azo type, condensed azo type, diimmonium type, phthalocyanine type, and anthraquinone type dyes are cited. As concrete examples of the near infrared ray abosorbing agent, polymethine type, phthalocyanine type, naphthalocyanine type, and metal complex type agents are cited. As the solvent for dissolving the main component, ketone type solvents such as cyclohexanone, ether type solvents, and ester type solvents such as butyl acetate, and ether alcohol type solvents such as ethyl cellosolve are enumerated as available.
The plasma display is required to use a near infrared ray absorbing agent capable of absorbing wavelengths of 850–1,100 nm for the purpose of preventing the remote control device from malfunctioning and is also required to absorb the so-called light of neon orange color emitted while the neon atom once excited is returned to the normal state. Since the conventional technique still falls short of absorbing this neon orange color fully sufficiently, the desirability of developing a technique which is capable of improving contrast has been finding popular approval.
Particularly, the dye which absorbs the neon orange light possibly reveals deficiency in heat resistance and humidity resistance and the deterioration of the dye possibly results in degrading the contrast along the course of time. Thus, the provision of an optical filter excelling in heat resistance and humidity resistance has been yearned for strongly.